Kazusa Province was a province of Japan in the area of modern Chiba Prefecture. The province was located in the middle of the Bōsō Peninsula, whose name takes its first kanji from the name of Awa Province and its second from Kazusa and Shimōsa provinces. Its abbreviated form name was Sōshū (総州) or Nansō (南総). The borders of Kazusa Province were defined by Shimōsa Province to the north, the Pacific Ocean to the east, Awa Province to the south, and Tokyo Bay to the west.

Chiba Prefecture is a prefecture of Japan located in the Kantō region of Honshu. Chiba Prefecture has a population of 6,278,060 and has a geographic area of 5,157 km2 (1,991 sq mi). Chiba Prefecture borders Ibaraki Prefecture to the north, Saitama Prefecture to the northwest, and Tokyo to the west.